Non-Polarized 3rd Gen lenses seem to not fit more times than they do, most only kinda fit in that the lower portion of the lens tends to sink past the frame towards your eyes and overall feel loose. While the polarized lenses seem to work better over the non-polar ones. Frogskins LX are slightly taller (?) in size I think, so they as though hook into the lower portion better.
Although there's no exact answer, as I've had lenses work on one 1st gen but not the other - but it seems LX lenses were the most consistent in fitting.